Generally, a color cathode ray tube includes an evacuated glass envelope having a funnel with a neck and a panel. An electron gun is housed in the neck and includes a cathode and a plurality of electrodes supported by supporting beads. A shadow mask is installed within the panel and spaced from the screen.
On the rear end of the neck, a plurality of terminals are provided for transmitting a video signal and a focusing voltage to an electron gun. On the outer surface of the funnel, an anode cup is electrically connected to an anode electrode which is a final accelerating electrode of the electron gun.
In the cathode ray tube, the electron gun is operated by a video signal and a control voltage applied through the terminals on the rear end of the neck and the anode cup of the funnel. A picture is displayed on the screen upon arrival of the emitted electron beam from the electron gun. As noted above the electron gun is mounted within the neck of the cathode ray tube. Voltages of very low potential are applied to the inner surface of the neck and voltages of very high potential are applied to the focusing anode. As a result, an arc may be generated by leakage currents formed within the inner surface of the neck. The leakage currents travel longitudinally through the spaces which are referred to as bead channels, between the electrode supporting beads and the inner surface of the neck.
A method for suppressing an arc generated by the leakage currents is disclosed in U.S. Pat. No. 4,338,543 and the device shown herein in prior art FIG. 4.
FIG. 1 illustrates a broken away perspective view of the neck portion 11 of the cathode ray tube 20 of the prior art (see FIG. 4) wherein there is provided an electron gun 10. A metallic band 15 is banded around supporting beads 14 near the focusing electrode 13. A focusing voltage, which is lower by thousands of voltages than an anode voltage, is applied to the metallic and 15, which is electrically connected to the focusing electrode 13.
Although, not shown here, a cathode ray tube for suppressing leakage currents causing an arc has been disclosed in U.S. Pat. No. 4,353,006 wherein, instead of the metallic band, a metallic coating layer is formed on the surface of the supporting beads.
However, since the aforesaid conventional arc suppressing means are provided by a process separate than the manufacturing process of the electron gun, the manufacturing efficiency is reduced and the manufacturing complexity and cost are increased.